lovely thread Thrall....
The hard questions in my opinion are the most important to ask. i have tended to find that if i find a question very difficult to ask it is because i am usually not sure that i want to know the answer. And these are possible relationship changing questions. If the answers are not what you need/hope them to be, it will affect the outcome of the relationship. Therefore, i would suggest asking them immediately. And as many have said, be prepared for an honest answer, wether it is what you wanted to hear or not.
i love Tom's suggestions for the STD question. And in this day and age, it is so important. And another important point to remember is that some of the STD's out there these days have a six month to a year 'incubation' period. So just because someone is tested one month into the relationship and everything is negative, it does not mean they can't convert later on. My suggestion would be condom use until after a year of a monogamous (sp?) relationship, and you both should be tested at six months and at a year. At that point if everything is negative, perhaps you can ditch the rubber raincoat!
As i was once told, the only dumb question is the one that doesn't get asked. Be prepared for an honest answer. In any relationship, if a person is condemned for answering honestly, their answers tend to become what they know someone wishes to hear instead of what they truly mean. i believe that is human nature to avoid conflict.
Good luck on your meet thrall!